The present invention relates to a rotary head cylinder designed to suppress the generation of noise when a magnetic head passes a separating position thereof from a tape to thereby to improve recording sound quality.
A projection is provided at a part of a conventional VTR cylinder where a tape is separated from the cylinder so as to reduce the jitters. In consequence, the running tape levitates from the surface of the cylinder short of the projection, giving rise to a distortion when a magnetic head passes the position short of the projection. The resultant snap-through phenomenon invites vibration of the tape, which accompanies undesirable noises. When recording, the noises caused by the vibration are recorded through a recording microphone to adversely influence the sound quality.
The structure of a conventional rotary head cylinder will be depicted hereinbelow. FIG. 5 is a perspective view of a conventional rotary head cylinder seen from the direction of a tape separating position. In FIG. 5, a magnetic head 7 is provided between a rotary cylinder 1 and a fixed cylinder 2, and is rotated along with the rotary cylinder 1 in the direction of an arrow A. A tape 4 is spirally wound around the outer peripheral surface of the cylinder by a guide post 3. The magnetic head 7 moves away from an upper edge of the tape 4. A projection 5 is provided in the vicinity of a point where the tape 4 is detached from the magnetic head 7 to thereby to reduce the jitters. FIG. 6 is an enlarged view of an area B of FIG. 5, showing the distortion of the tape generated when the magnetic head passes the position of the projection. FIGS. 7A and 7B are waveform diagrams of the time response and the frequency response obtained when noises is measured in the vicinity of the tape separating point.
In a general rotary head cylinder of the above structure, as shown in FIG. 5, the disturbance of an image, called the jitters, is reduced by means of the first projection 5 provided at a part on the fixed cylinder 2 where the tape 4 is separated from the magnetic head. The projection 5 projects somewhat more than the magnetic head 7, lifting the tape 4 above the surface of the cylinder 2 at the point where the magnetic head 7 is separated from the tape 4, so that the magnetic head 7 is smoothly separated from the tape 4. In this manner, the jitter is decreased as the vibration of the tape 4 is reduced. However, the projection 5 causes the upper edge of the tape 4 to levitate from the surface of the cylinder, and therefore the tape 4 is partially deflected, as represented by C in FIG. 6, immediately before the magnetic head 7 passes the point. The distortion is further spread along with the advancement of the magnetic head 7. When the distortion is relieved, the snap-through phenomenon is brought about, thereby suddenly deforming the tape 4 as much as if the tape sprang. The tape 4 is partially vibrated as a result of the deformation impact. The effect of reducing the jitter with the projection 5 is eliminated. At the same time, noises are generated synchronously when the magnetic head 7 passes the point, as indicated by D in FIG. 7A. The noises are taken through a recording microphone when recording, and the sound quality is badly influenced. This imposes a real obstacle to achievement of a miniature and high-fidelity VTR, particularly, a camcorder having a microphone and a mechanism of a driving system incorporated together therein.